High frequency modulation system



Nov. 5, 1935. I L. M. APPLEGATE HIGH FREQUENCY MODULATION SYSTEM FiledApril 5, 1930 source 0/ FIGURE I ZZZ/emf m? any cm 72 k f FIGURE. 1!!

ZZZ/emf V INVENTOR: LINDSAY M. APPLEGATE,

BY f M,-

. ATTORNEYS.

Patented Nov. 5, 1935 UNITED STATES HIGH FREQUENCY MODULATION SYSTEMLindsay M. Applegate, Seattle, Wash., assignor,

by mesne assignments, to Collins Radio Company, Cedar Rapids, Iowa, acorporation of Delaware Application April 5, 1930, Serial No. 441,961

10 Claims.

My invention relates to the use of small changes in electrostaticcapacity forthe control of electric circuits. The purpose of myinvention is to produce a circuit in which the magnitude and changes. inmagnitude of electrostatic capacity of two adjacent conducting platescontrol, respectively, the magnitude and changes in magnitude of anelectric current.

While my invention is broadly related to electrical control systemsgenerally, I have selected the application of my invention to highfrequency modulation systems as one method of illustrating my invention.

The basic and other features of my invention will be described in thespecification to follow and will be succinctly defined in the appendedclaims.

In the accompanying drawing,

Figure I is a diagrammatic view illustrative .of my invention in anarrangement for the control of 2 magnitude of current.

Figure 11' is a similar view showing, for purposes of illustration, myinvention in an arrangement for the control of magnitude and directionof current.

25 Figure III is a similar view illustrative of an application of myinvention in a balanced circuit arrangement for the control of themagnitude of current varying from zero.

Referring to the numerals on the drawing, l

30 indicates a source of high frequency alternating current, preferablyof a frequency of the order of 1,000,000 cycles per second or any othercon venient high frequency, 2 indicates a resistor, preferablynoninductive, which, in connection 35 with the high frequency source I,provides for a definite regulated voltage at its terminals. This voltageis impressed upon a circuit embracing a condenser 3 and a resistor 4,preferably noninductive;

Condenser 3 consists, preferably of two plates in electrostaticrelationship arranged so that the distance, and hence the electrostaticcapacity between them is variable. High frequency electric current willflow in the part of the circuit embracing condenser 3 and resistor 4.The intensity and phase of this current will be dependent upon thecapacity of condenser 3 in accordance with well known electrical laws.Furthermore, if the current that flows through resistor 2 is large in 50comparison with that flowing through condenser, 3 and resistor 4 and theimpedance of condenser 3 is large relative to the impedance of resistor4, the current through 3 and 4 will be approximately proportional to thecapacity of condenser 3, hence,

55 proportional to the distance between the plates of condenser 3. Thehigh frequency voltage between the terminals of resistor 4 will beproportional to the current in resistor 4. The voltage of resistor 4 isimpressed on the grid of an amplifier 5. Resistor 4 provides formaintaining the 5 grid bias of amplifier 5 as well as providing the highfrequency alternating voltage.

The usual appurtenances of amplifiers are understood to be presentalthough not shown in Figure I. l0

Amplifier 5 delivers energy through a transformer 6 to a detector 1. Theoutput of amplifier 5, when properly adjusted, is substantiallyproportional to the high frequency alternating voltage impressed uponits grid by the resistor 4. 15 The output of detector l is substantiallyproportional to the envelope of the high frequency alternating voltageof resistor 4, and hence to the distance between the plates of condenser3.

The intensity of the current of detector 1 is indicated or recorded by aterminal apparatus 8. The result of the action of the arrangement shownin Figure I is to provide an indication by mechanical action in theterminal apparatus 8 proportional to the movement in the relativeposition of the plates of condenser 3.

The action of this form of my invention may be summarized as follows.

The relative position of the plates of condenser 3 is represented in theoutput circuit of the detector 1 by the intensity of the output current.The rate of change in the relative position of the plates of condenser 3is represented in detector 1 by the rate of changeof output current.This may be expressed in the statement that the output current ofdetector I is modulated by the relative movement of the plates ofcondenser 3. Any movement, oscillation, pressure, or impact within therange of the apparatusca-pable of changing the relative position of theplates of condenser 3 can be measured or recorded'by the arrangementshown in Figure I.

If the relative movements of the plates of condenser 3 in Figure I areof the nature of oscillation resulting from the action of impingingsound waves, the output of the detector I may be used in conventionalaudio circuits. This is indicated in Figure I in which the output ofdeoriginal sound by a telephone receiver. It is obvious that thetelephone receiver could be replaced by any other apparatus requiringaudio frequency current.

In another form of my invention, illustrated in Figure 11, variations inthe relative positions of the plates of condensers l3 or 23, or both,produce changes in polarity and consequent reversal of action as well aschanges in magnitude of current in the terminal apparatus.

In Figure 11, l is a source of high frequency electric energy. l2 and 22are resistors, preferably noninductive. l3 and 23 are condensers arangedso that when the capacity of one increases the capacity of the otherdecreases or remains fixed. i4 and 24 are resistors preferablynoninductive. l5 and 25 are amplifiers. I8 is a coupling betweenamplifiers l5 and 25, and detectors I1 and 21. I8 is a polarized relayarranged in such a way that if the magnetomotive force of the coilassociated with detector I1 is equal to that of the coil associated withdetector 21, the contacts l9a and I9?) are open. If the magnetomotiveforce of the coil associated with detector I I is greater than that ofthe coil associated with detector 21 the contact lSa is closed, if lesscontact 1% is closed. Under most conditions of application, the actionof the circuit shown in Figure 11 will be to close either contact lea orcontact I9b, depending upon the relative capacities of condensers l3 and23. It is obvious that if half the duplicated elements in Figure 11 areremoved, the circuit will then be the same as that of Figure I, exceptthat the indicating device 8 will have been replaced by a relay.

Figure III shows a modification of my invention in which a source ofhigh frequency energy i is connected with a balanced circuit whichincludes resistors 32 and 42 and condensers 33 and 43 arranged so thatunder certain conditions the voltage impressed on a resistor 34, whichmay be inductive, is substantially zero. With a change in eithercondenser 33 or 43, or both, the balance will be disturbed so that avoltage will appear at the terminals of resistor 34 which will be am-'plified by a relay 35, whose output will be delivered by a transformer36 to a rectifier 31 whose output will operate a relay 38. Thisarrangement is capable of responding to very small changes in distancerepresented by changes in the spacing of the plates of condenser 33 orof condenser 43, or preferably, both for maximum of effect, or theincrease of one and decrease of the other, or by changes in capacitydue, for example, to changes in pressure, temperature, or composition ofthe dielectric of condenser 33 or of condenser 43.

What I claim is:

l. The method of modulating a high frequency alternating current whichcomprises delivering an unmodulated high frequency current to anaperiodic branched circuit containing conducting and phase shiftingelements, said unmodulated high frequency current being divided betweena first branch of said circuit and a second branch of said circuit, thecurrent in the: said first branch being large in comparison with thecurrent in the said second branch, altering the impedance of said phaseshifting elements by differential variation thereof in accordance withsignal energy for effecting modulation of said high frequency current insaid second branch of said circuit.

2. A modulating system comprising a source of high frequency alternatingcurrent, a branched modulating circuit including a multiplicity ofresistors and a pair of differentially variable condensers, said sourceof high frequency alternating current supplying an unmodulated currentto a plurality of said resistors, said pair of differentially variablecondensers operative to produce a modulated high frequency current ineach of a 5 second plurality of said resistors, an amplifier circuit anda detector circuit connected with each of said second plurality ofresistors, means for combining the outputs of said detector circuits,and a utilization circuit connected with said combining means.

3. In a system for utilizing the variations of a pair of differentiallyvariable phase shifting elements the combination of a circuit containinga first pair of resistors of low impedance, a second 15 pair ofresistors of relatively high impedance and a pair of differentiallyvariable phase shifting elements, means for delivering to said firstresistors unmodulated'high frequency altemating current, means includingsaid phase shifting elements for delivering modulated currents to saidsecond resistors, and means including said second resistors forimpressing modulated voltages on the input elements of a pair ofutilizing circuits.

4. In a system for utilizing the variations of a pair of difierentiallyvariable phase shifting elements the combination of a circuit containinga first pair of resistors of low impedance, a second pair of resistorsof relatively high impedance and 30 a pair of difierentially variablephase shifting elements, means for delivering to said first resistorsunmodulated high frequency altemat-. ing currents, and means includingsaid second resistors for impressing modulated voltages on 35 the inputelements of a pair of utilizing circuits, said second resistors actingas biasing connections for said utilizing circuits.

5. The method of modulating a high frequency alternating current whichconsists of delivering 40 an unmodulated high frequency current to abranched circuit containing conducting and differentially variable phaseshifting elements, causing one of said branches to carry a substantiallyunmodulated high frequency current and another 45 of said branches tocarry a high frequency current modulated by the action of saiddifferentially variable phase shifting elements, producing thereby ausable modulated high frequency potential'difl'erence across aconducting element 50 of said latter-branch.

6. A modulating system comprising a pair of parallel circuits, a firstof said parallel circuits including a pair of resistance elements, asecond of said parallel circuits including a pair of dif- 55 ferentiallyvariable condensers, means for impressing a high frequency alternatingcurrenton said'parallel circuits, and means comprising saiddifferentially variable condensers-for modulating said high frequencycurrent. 60

'7. A modulating system comprising a pair of parallel circuits, a firstof said parallel circuits including a pair of resistance elements, asecond of said parallel circuits including a pair of differentiallyvariable condensers, means for im- 65 pressing a high frequencyalternating current on said parallel circuits, an output circuitresistively coupled with said second parallel circuit, means comprisingsaid differentially variable condensers for modulating said highfrequency 7 current, and means for delivering said modulated current tosaid output circuit.

8. A modulating system comprising a pair of parallel circuits, a firstof said parallel circuits including a pair of resistance elements, asec- 15 0nd of said parallel circuits including a pair of differentiallyvariable condensers, means for impressing a high frequency alternatingcurrent on said parallel circuits, a pair of balanced output circuitscoupled to said second parallel circuit, means comprising saiddifferentially variable condensers for modulating said high frequencycurrent, and means for delivering said modulated current to said outputcircuits.

9. A modulating system comprising a Wheatstone bridge-arrangement, apair of relatively low resistances composing two of the arms ofsaidbridge, a pair of difierentially variable condensers composing the othertwo arms of said bridge, a separate source of high frequency alternatingcurrent, means for supplying said source to opposite terminals of saidbridge arrangement, a relatively high resistance element, meanscomprising said differentially variable condensers for modulating saidhigh frequency current, and means for delivering said modulated highfrequency current to the terminals of said high resistance element andto a utilizing circuit.

10. A modulating system comprising a pair of parallel circuits, a firstof said circuits containing resistance of relatively low value, a secondof said circuits including at least one variable condenser andresistance of relatively high value, an external source of unmodulatedhigh frequency alternating current, means for supplying said highfrequency current to said parallel circuits, means including saidvariable condenser for modulating the high frequency current in saidsecond parallel circuit, and means including said 15

